418 



MESOZOIC ERA— AGE OF REPTILES. 



Labyriniliodonts have already been described, in connection with 

 the Carboniferous when they first occur. They culminate, however, in 



size and in com- 

 plexity of tooth- 

 structure' — if not 

 in number and 

 variety — in the 

 Triassic, and then 

 become extinct. 

 Fig. 612. In some cases they 



reached gigantic 

 proportions. The 

 head of the Mas- 

 todonsaurus (Fig. 

 615) w T as three 

 feet long and two 

 feet wide. The 

 tooth of the typi- 

 cal genus Labyrinthodont was three and a half inches long and one and 

 a half in diameter at the base (Fig. 617). The complex labyrinthine 

 structure is shown in Fig. 618. Attention was first drawn to these 



Fig. 613. 



Fig. 614. 



Figs. 612-614.— Triassic Fishes: 612. a, Dental Plate of Ceratodus ser- 

 ratus; b, Dental Plate of Ceratodus altns. Keuper (after 

 613. Acrodus minimus. 614. Hybodus apicalis (after Agassiz). 



Fig. 616. 



Figs. 615, 616.— Triassic Reptiles— Labyrwthodonts : 615. Mastodonsaurus Jaegeri. 616. Trema- 



tosaurus (after Huxley). 



